Field of the Invention
The present invention relates to a shield and a helmet.
Related Art
The present invention relates to a shield for a helmet worn by a motorcycle rider and a helmet installed this shield.
Each motorcycle rider is required by law to wear a helmet for protecting the head at the time of possible occurrence of an accident. Such a helmet has also a function of shielding, to a certain extent, various jarring noises such as an engine sound, an exhaust sound, and a wind noise generated when traveling of a motorcycle.
Among these kinds of noises, the engine sound and the exhaust sound contain relatively high frequency components and hence are considerably reduced when passing through the helmet. In contrast, the wind noise is a sound generated by friction between air and the motorcycle or the rider's body and contains relatively low frequency components. Thus, even after passing through the helmet, the wind noise is hardly reduced and serves as a large trouble for the rider. Here, it is known that the wind noise is generated in association with a situation that the layer of air flowing along the outer surface of the helmet departs from the helmet in a rear part so as to form the air current.
In recent years, the structures of a ventilator for air intake and air exhaust or a stabilizer for air rectification and the like attached to the outer surface of a full face type helmet are complicated or their sizes are increased. Such a ventilator and a stabilizer swirl a traveling wind and increase remarkably the intensity of the wind noise. Thus, the wearers of the full face type helmets hear such a loud wind noise.
On the other hand, along with such a noise, the aerodynamic characteristics of the helmet are an issue. That is, the following three forces are generated and act on a helmet during a running: a lift force which is a force acting in a direction at right angles to the air flow such as to lift up the helmet; a drag force acting in parallel to the air flow such as to push the helmet in a direction opposite to a traveling; and a yaw force acting such as to pull the helmet sideways. Improvement of the aerodynamic characteristics such as the lift force, the drag force, and the yaw force is also required.
Patent Document 1 describes a configuration that depressions and protrusions are provided in the surface of a helmet in order to reduce the fluid resistance acting on the helmet wearer as a result of a remarkable air resistance at the high speed running. That is, like in a golf ball, depressions and protrusions (dimples) are provided in the entire surface of the helmet so that the air resistance is reduced.
Patent Document 2 describes a configuration that depressions and protrusions are provided in the outer surface of a helmet in order to reduce a noise generated close to the ears. In this configuration, the processing is performed on a half of the entire surface of the helmet so that an effect of reducing the air resistance is intended similarly to Patent Document 1.
Patent Document 3 describes a helmet in which dimple processing is performed on an upper part of a shield. Since, with increasing speed, the rider takes a more frontward-leaning posture and hence the site hit by a running wind becomes close to the position of the forehead of the helmet wearer, that is, an upper part of the shield and an upper part of the helmet (around the forehead of the wearer). Thus, a structure is arranged in the vicinity of the boundary between the shield and the helmet upper part so that the surrounding turbulence is divided into several pieces and thereby the air resistance is reduced.